1. Field of the Invention
This invention relates to a radio communication apparatus, a communication control method, and a computer-readable program.
2. Description of the Related Art
USB memories are known as devices which have been frequently used for apparatuses which include USB (Universal Serial Bus) interfaces (I/F). USB memories have been generally used to share, exchange and transfer data. USB memories are nonvolatile memories which can be portable.
USB memories do not depend on the specification of a host terminal of a personal computer (PC) or the like, and can be immediately identified by the host terminal when connected to the USB I/F of the host terminal. Thus, USB memories are easily used as external memories. This convenience is the reason whey USB memories are frequently used. A user can save a file of a presentation document in a USB memory at an office, and open the file by connecting the USB memory to a PC at a meeting place for presentation. Also, when the USB memory is connected to the host terminal with a wire (cable), electric power is supplied via the USB I/F of the host terminal, and thus a power circuit is not necessary.
Recently, short range radio communication technologies have been developing and radio communication systems have been spreading instead of conventional cable communication systems home and office communication networks. In particular, the wireless USB which applies an UWB (Ultra Wide Band) system can perform high speed transmission and reception of data of large capacity in comparison with radio communication systems such as Bluetooth (a registered trademark), wireless LAN (Local Area Network) or the like. The wireless USB is expected to be a radio communication technology of the next generation. The wireless USB is a communication system which establishes, in advance, a “host” (e.g. a PC and a game machine) and a “device” (the peripheral equipment which is to be connected to the host.) as a master-slave relationship between the communicating devices. The wireless USB communication system is different from the other radio communication systems which assumed many-to-many communication. The network of the wireless USB reduces a circuit scale by restricting the network formation to one-to-many connection. In general, a procedure to determine this master-slave relationship is called an “association”. The wire association is performed by connecting a host with a device using a USB wire before performing radio communication, and the numeric association is performed by inputting numbers displayed on a terminal.
FIG. 1 shows a flow diagram describing a conventional association procedure of a wireless USB. In step S1001, a host notifies a device of a CHID (Connection Host ID) which is identification information to identify the host. In step S1002, the device stores the received CHID in a memory (e.g. a nonvolatile memory) of the device. Subsequently, in step S1003, the device notifies the host of a CDID (Connection Device ID) which is identification information to identify the device. In step S1004, the host generates connection information CC (Connection Context) which includes the CHID which is the host's identification information, the CDID received from the device, and an association information CK (connection Key) which associates the host and the device to each other, and the host notifies the device in step S1005. Finally, in step S1006, the connection information CC is stored in the memories of the host and the device, respectively. In this manner, the connection information CC is shared by the host and the device, and thus association is completed.
In such circumstances, USB memories which are conventionally used in cable communication are desired to be developed into a radio communication system. Developing the radio communication system of USB memories is convenient when the USB I/F of a host terminal exists at a place where USB memory cannot connect and when the USB memory cannot be transferred from a specific place based on a security reason. Further, a host terminal can avoid a problem of connecting the USB memory by a cable.
A USB memory key using a function of a wireless transceiver is disclosed in the Japanese Patent Application Publication 2006-268831 (patent documents 1). This USB memory key can establish a radio link with an apparatus by placing the USB memory in a wireless effective range of the apparatus which is a communication partner, such as a computer or the like.
Further, an apparatus is disclosed in Japanese Patent Application Publication 2006-238413 (patent documents 2), in which the apparatus can switch from a cable USB standard communication method to a radio communication method different from the cable USB standard. Also, a procedure of the communication between radio host USB devices is disclosed in the patent document 2.
However, for technologies for developing radio communication systems disclosed in the patent documents 1 and 2 described above, there is a problem in that a process to establish a radio link is complicated. As described above, it is necessary for radio communication of the wireless USB to establish “host” and “device” as a master-slave relationship between apparatuses (devices) by an association in advance of performing radio communication. In such a relationship, a device needs to find a host accepting a new connection to establish a radio link between the host and the device, and needs to send a connection request to the host.
Further, since a USB memory cannot receive power supply from a host terminal, when connected to the host terminal by radio (different from the case of cable connection), the USB memory needs to include a built-in battery. For maintaining the lifetime of the battery, it is important to minimize unnecessary power consumption.
This invention takes into consideration the issues above, and relates to a radio communication apparatus, a communication control method, and a computer-readable recording medium having a communication control program, which provide automatic establishment of a radio link according to the radio communication protocol based on the relationship between a host and a device, and when there is no data communication, power supply from a battery of the device is automatically terminated.